Changes must be made to a law that is blocking the inquest into the shooting of a man whose death led to a wave of rioting last summer, says the police watchdog.
The Independent Police Complaints Commission (IPCC) says there must be more transparency in cases where people are killed by officers – as in the case of Mark Duggan.
It said sections of the Regulation of Investigatory Powers Act, which can bar intercept evidence from being made available to coroners were an “obstacle”.
The comments come as it was revealed an inquest into Duggan’s death could be impossible because of “disclosure issues” surrounding police evidence.
The IPCC may have material "that it could not properly disclose to a coroner" over the decision by officers to shoot Duggan, North London Coroners' Court was told.
In a statement to BBC 4’s Today programme, deputy chairman Deborah Glass said the body was “frustrated” when “anyone or anything” gets in the way of its ability to provide information or ensure cases are heard fully in public.
Without directly referencing the Duggan case, the statement said: "The IPCC believes that it is essential for families to play a full part in any process which establishes how and in what circumstances their family member died.
"Our principal statutory duty is to secure and maintain confidence in the police complaints system and one way in which this can be achieved is by ensuring that there is proper public scrutiny when someone dies at the hands of the state."
A coroner's officer said a provisional date of January 28 has been set for proceedings - but only if the eight-week inquest is given the go-ahead during a review on October 23. An alternative could be a special inquiry where some evidence is heard behind closed-doors, it is understood.
An IPCC spokeswoman confirmed that issues relating to the submission of sensitive evidence were being discussed by the coroner.
Both the watchdog and Scotland Yard have admitted mishandling the way they dealt with Duggan's family.
Initial reports that Duggan shot at police were dismissed by ballistic tests which later found that a bullet which lodged itself in one officer's radio was police issue.
Duggan was a passenger in a minicab when he was killed during a pre-planned operation involving officers from the Metropolitan Police Trident gun crime unit on August 4 in Tottenham, north London.
But police failed to formally notify the family of his death, giving his parents Pamela Duggan and Bruno Hall false hope.
Relatives subsequently complained about their treatment which was upheld by the IPCC.
The IPCC is still conducting a separate investigation into the circumstances of the shooting, with an investigation into his death failing to establish the sequence of events concerning a handgun found at the scene.